Transparent to translucent flame-retardant polycarbonate composition

#This invention is directed to an improved transparent to translucent flame-retardant polycarbonate composition. More particularly, this invention is directed to a high molecular weight aromatic polycarbonate containing in admixture therewith: (a) an alkali or alkaline earth metal salt of an organic sulfonic acid, or mixtures of said salts; and (b) a coadditive that acts as a solvent for said salts or mixtures thereof, said compositions exhibiting improved optical characteristics over those containing only said salts while maintaining high flame retardancy.

#With the increasing concern for safety, there is a need to provide safe materials for public and household use, including flame retardant transparent or translucent products for use by the consumer. As a result, many products are now required to meet certain flame retardant criteria byy local and federal governments as well as by the manufactures of such products. One set of conditions employed as a standard for measuring flame retardancy is set forth in Underwriters' Laboratories, Inc. Bulletin 94 pursuant to which materials are rated for flame retardant characteristics.

#In the art, there are many known flame retardant additives which are employed by mixing them with the products to be rendered flame retardant. Such flame retardant additives have been known to be employed in amounts of about 5 to 20 weight percent in order to be effective to resist burning of those products with which they are employed. It has been found, however, that at these concentrations these flame retardant additives can have a degrading effect upon the products with which they are employed, thereby often resulting in the loss of valuable physical properties of the base product. This is particularly evident when known flame retardant additives are employed with polycarbonate resins, as many of these additives have a degrading effect upon the polymer.

#The following examples are set forth to illustrate the best mode currently known to practice the invention. Unless otherwise specified, parts or percents are by weight.

#One hundred parts of a high molecular weight aromatic polycarbonate powder, prepared by reacting 2,2-bis(4-hydroxyphenyl) propane (bisphenol-A) and phosgene in the presence of an acid acceptor and a molecular weight regulator and having an intrinsic viscosity of 0.57 dl/g in methylene chloride at 25.degree. C., was mixed with 0.2 parts potassium diphenylsulfone-4-sulfonate in finely divided form. The resulting mixture was then fed to an extruder which was operated at about 265.degree. C., and the extrudate was comminuted into pellets.

#The pellets were then molded at about 315.degree. C. into test plaques measuring 2 in. by 3 in. by 0.062 in., using conventional molding techniques. The optical properties of the test samples were measured using the G. E. Recording Spectrophotometer and haze determinations were made on Gardner Hazemeter. The results obtained are set forth in the Table.